Steady locomotion in torso-actuated rimless wheel robots

Rimless wheel robots are ground robots whose wheels have no rims or tires but only spokes. This paper considers torso-actuated wheel robots. Each robot considered in this paper is composed of a single wheel and a single torso connected to the wheel centre by an actuated revolute joint. There have been proposed several controllers for torso-actuated rimless wheel robots; however, their locomotion properties are poorly understood. For example, similarities and differences between the rimmed and the rimless wheel robots are unknown. This paper first investigates steady locomotion of a torso-actuated rimmed wheel robot theoretically. Then, steady locomotion of a torso-actuated rimless wheel robot is evaluated for various parameters by numerical simulations. Finally, similarities and differences between the rimmed and the rimless wheel robots are discussed. In particular, it is shown that the speed-maximizing posture is substantially shared among the rimmed and the rimless wheel robots. On the other hand, some other properties are not shared among them. The most significant difference is the relationship between the maximum steady speed and the wheel radius. It is concave in some parameter space for the rimless wheel robot, but is linear in the whole parameter space for the rimmed wheel robot.